Elastomeric molded gaskets have been conventionally used for resiliently supporting a sewer pipe in an opening through the wall of a manhole, for example. Such gaskets provide a watertight seal, closing the space between the wall of the opening and the pipe.
Extruded gasket rings described in U.S. Pat. Nos. 3,813,107, 3,796,406 and 3,832,438 have been utilized for supporting sewer pipes of substantial size by means of a gasket having a hollow nose section integral with a base member which is embedded in the manhole when cast. Such gaskets are made by cutting a length of a linear extrusion to a size corresponding to the circumference of the pipe, curving the cut length into the form of a cylinder, joining the ends and flattening the wall to produce a disk-like washer-type gasket which must be held against considerable internal stress until the cast material sets. The strains involved in producing gaskets of relatively small diameter, such as of the order of four (4) to six (6) inches, limits the use of small diameter sizes.
Another type of gasket is the molded gasket which is shaped like an ordinary washer, i.e. is comprised of an apertured disk lying in a single plane having its outer margin embedded in the cast material and lies in a plane which is substantially perpendicular to the axis of the pipe extending through the gasket. These gaskets have limited stretch in the outward radial direction and even though the gaskets can be made with an undersized hole so that the pipe will stretch the material on being inserted, the amount of stretch is insufficient, in the plane of the gasket to provide enough freedom for distortion in order to preserve a tight seal.
Molded gaskets of the above-mentioned type also are limited as to the amount of deflection which a conduit may undergo from a nominal desired position of alignment and further have limited ability to accommodate large variations in pipe diameter which is disadvantageous for a number of applications.
A gasket which solves some of the above problems is described in U.S. Pat. No. 4,103,901, issued Aug. 1, 1978 and assigned to the assignee of the present invention. The gasket described in this patent is sufficiently resilient to compensate for shear stress, is sufficiently flexible to accommodate extensive misalignment of the pipe and yet is capable of affording an absolutely fluid tight seal in the rim of the opening and is easy to install, comparatively inexpensive to manufacture and has a long useful operating life.
The gasket of U.S. Pat. No. 4,103,901 has a peripheral flange structure which is embedded into the cast material and comprises an outer band and an integral radially extended web forming a substantially T-shaped configuration. The gasket extends inwardly therefrom defining an outer skirt portion which is reversibly angled to form an inner skirt portion integrally joined to the outer skirt portion at a pleat or fold. The inner skirt extends generally diagonally inwardly from the fold toward the center of the gasket and terminates in a annular-shaped beaded inner end of an O-ring configuration. The gasket, however, is unidirectional in that the conduit inserted into the gasket opening can only be pushed in one direction. The "memory" of the gasket is such that the pleat or fold is not capable of being reversed so as to enable the O-ring portion of the gasket to be selectively positioned on either of two "over-center" positions relative to an imaginary intermediate position. More specifically, the pleat is molded into the gasket in such a manner as to be incapable of being reversed.
U.S. Pat. No. 4,903,970, issued Feb. 27, 1990 and assigned to the assignee of the present invention discloses a gasket arrangement in which the gasket is capable of being moved between a folded or pleated condition to an unfolded condition achieved by providing two skirt portions of unequal length which enable the gasket to be folded or unfolded but does not permit the gasket to be folded in the same manner either of two opposing directions.
All of the above designs suffer from the disadvantages of being incapable of being easily moved to either of two over-center positions and to either of two opposing folded states.